TPU orientation

[Samsquanch]

Newbie here with what is probably an obvious question. So I’ve got my Skeena pieces cut out. Got my tools ready. Tested my welding technique. Watched a bunch of videos. Feeling more or less ready to start welding my first DIY packraft. I have this nagging question. When you are joining two pieces of fabric, is there a principal that guides how the fabric faces should be oriented to each other? For example, on the inflation bag, the circular piece of 1000D could have it’s TPU facing the TPU coating of the 40D, or it could be oriented with the TPU facing the fabric. You mention the risk of melting the TPU on the far side which suggests the latter, but then would the bond not be stronger if they aligned TPU to TPU? I was initially confused with the same question when considering how R3 would orient to the floor. In that case it’s the TPU of the walls onto the fabric side of the floor. The videos are very helpful in this case, but I haven’t seen orientation mentioned directly anywhere.

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[androidmids]

So when welding the floor material which is double coated, how can we melt it to itself if we cannot weld tpu coated sides of fabric?

[Matt (Admin)]

There’s no step in the DIY Packraft kits where that’s required, but in theory you could use a hot air welder.

[Samsquanch]

Thanks for the response. That totally makes sense. It was the fact that the heavier fabric is coated on both sides that I’d missed. I was able to build confidence by watching the videos, but found myself pausing the videos at various points to check if the floor was shiny side up or down. My Alpacka has the floor shiny side up, which was also giving me pause. In the end I just went for it and so far so good.

[invincible]

Excellent, that’s super helpful!  I had the same question when I just started my build yesterday.  I just went with what was shown in the videos and figured it must be working.  I did notice that if you touch the iron to either side of the black floor fabric it looked like it was melting, whereas it only did that to one side of the colored fabric.  Now I know the ‘science’ behind it.

[Matt (Admin)]

Sorry for the confusion – I guess I need to make this clearer somewhere (or maybe several somewheres).

The lighter fabrics (e.g. tube fabrics, seam strips, inflation bag fabric) are coated with TPU on one side only, and the woven fabric is exposed on the other side.

The heaver fabrics that are used the in packraft floors are coated with TPU on both sides, so the orientation doesn’t really matter. The newer floor fabric presently used in the kits (the 450 GSM fabric) still has TPU on both sides, but one side has a glossy finish and the other has a matte finish, and I think that that difference in appearance is causing some people to assume only one side has a TPU coating.

When ironing the fabrics together, you can only press your iron against a surface that isn’t coated in TPU, so in any situation where you’re welding something to a piece of floor fabric, there’s only one way to do it (by pressing your iron on the woven fabric side of the other piece of fabric).

Does that make sense?

[Author]

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